An impregnated corrugated paperboard, a composition therefor, and a process of making said composition



Albert R. McManus, St. Louis, M0.

N Drawing. Application March 7, 1957 Serial No. 644,476

, 6 Claims. (Cl. 106-230) The invention relates to a new and useful impreghant for paperboard which increases the column loading strength to at least about 300 percent, and beam loading strength at least 200 percent regardless of humidity conditions.

The pcrsent invention comprises fully refined 133 F. melting point parafiin and limed rosin having about 4.5 percent lime content in the ratio of from 45 :55 to 55:45 respectively. The said mixture is prepared by charging substantially equal quantities by weight into a suitable vessel and heating to 325 F. with some occasional mild agitation. I have found that 180 p. s. i. steam in coils a safe and desirable method of melting the mixture and holding it at about 325 F.

in recent years there has been an increasing demand for an inexpensive strength imparting and water resistant paperboard impregnant to be used for fruit and vegetable containers which, in the field are subjected to high hum.dity conditions, and containers that are stacked many times out in warehouses for long periods of time.

Ordinarily the entire container is not impregnated as the surface of the impregnated paperboard is unsatisfactory for printing, etc. Therefore, impregnated liners or corner posts are placed inside the container to provide the increased top load strength required.

I have found that corrugated paperboard is most easily compositon do not materially stiffen the corrugated paperbers and not merely coating the surface thereof. To do I this, the impregnating composition must be highly fiuid at the application. temperature and of a nature to be absorbed into and cling tightly to the fibres and to fill all Y voids without shrinking upon cooling. Of course, in order that all mositure be driven from the fibreboard, the impregnating composition must be applied at a temperature higher than the boiling point of water, yet not so high as to burn or scorch the paperboard. I have found that a temperature of 325 F. is entirely satisfactory and safe, the flash point of my impregnating composition being over 400 F.

The objects of my invention are to provide an inexpensive water resistant and strength imparting impregnant for corrugated paperboard, a process of making it and the paperboard made therewith.

Another object is to provide a paperboard impregnant that increases the column loading strength of corrugated paperboard to at least about 300,percent.

Still another object is to provide an impregnant which will stiffen the paperboard without imparting an extreme brittle condition.

A further object is to provide an impregnant for paperboard containers which will not contaminate or damage articles packaged therein. v

A search for a satisfactory paperboard impregnant was made in which several inexpensive and water-proof materials were tested. Among the materials tested were:

1) Paraifin. (2) A mixture of wood rosin and paraifin. (3) A mixture-of wood rosin, parafiin and gilsonite. (4) Sulphur. All of the materials would be satisfactory costwise in the highly competitive paperboard industry. Results of these comparative tests are shown below in Table I.

Table I I rltilflgds Column Loading (percent) Beam Loading (percent) a e- Impregnating composition rial Applied 99% 24 hour 50% 99% 24 hour per M Rel. Rel. Water Rel. Rel. Water Sq. Ft. Hum, Hum., Immer- Hum., Hum, Immer- 72 hrs. 72 hrs. sion 72 hours 72 hours sion Untreated Board 100 61 0 100 50 0 ggZiWhige $61531? Paraffin 105 244 163 3 182 118 5 me on 0s1n White Refined Pamfi 125 341 325 47 223 204 41 50% Limed Wood Rosin 40% White Refined Parafiin 141 338 322 68 209 182 64 10% Gilsonite 100% Sulphur 236 354 321 30 232 186 32 NorE.Untreated board at 50% relative humidity equals 100%.

impregnated by immersing the corrugated paperboard into the impregnating composition in such a position so that the impregnating composition can flow freely through the flutes. The immersion time should be such that all bubbling and foaming ceases, indicating that all air and moisture has been driven from the paperboard. When the treated corrugated paperboard is removed from the vessel it must be supported so that all surplus impregnating composition can drain freely from the flutes and the paperboard surface as the corrugated paperboard will remain somewhat soft until the impregnating composition has cooled. Some care should be taken not to mash the flutes while draining.

I have found that surface deposits of the impregnating Parafiin alone increases column loading strength about 2 /2 times and the material used per thousand square feet of paperboard is approximately pounds. A mixture of 50 percent limed wood rosin and 50 percent paraffin on the other hand increases the column loading strength of corrugated paperboard approximately three and one-half times while using pounds per thousand square feet of paperboard, furthermore the strength is not materially reduced at 99 percent relative humidity as in the case of 100 percent parafiin. percent gilsonite is added to the limed wood rosin paraffin mixture, it further increases its strength at extreme wet conditions however, the addition of gilsonite does not increase the strength at other conditions and the ma- Patented Jan. 13;, va

When about 10 Table II.Parafi9n-.limed wood rsin'.f0r'mula variation Lbs..

. impreg hating composi-.

tion Absorbed For M Sq;

Column Loading- Ave'.,M2ix'. Load in Percent Lbs.

Limed, Wood Rosin Percent Paraflin Plain Paperboard.--

It is readily seen from Table II that as the ratio oflimed wood rosin to parafiin is increased, the column loading strength of corrugated paperboard likewise increases but ata progressively reduced rate while the quantity of impregnant absorbed per thousand square feet increases rapidly to an economically prohibitive amount. Further-- more at a ratio of limed wood rosin below--45%, to limed wood rosin has a tendency to drop out of the mixture. A ratio of from 45 :55 to 55 :45 of-paraflin to limed wood rosin respectively gives satisfactory column loading strength characteristics whilenotrequiring excessive quantities of materialperthousand square feet-of paperboard.

Therefore, by way of illustration, and not by way of limitation the following specific'formula has been found to produce excellent results:

Heat to 325 F.'with-some'occasional agitation to form a smooth homogeneous mixture.

It is understood that the embodiments herein described are illustrative and not restrictive, and it is also to be understood that the inventionrnay be susceptibleof embodiment in other modified forms, andtthat alltsuch modifications whichware. .similar. or. equivalent. hereto come equally within the scopeof the claims next appearing.

What I claim is:

1. A water resistant and strength imparting impregnating composition for application, to corrugated paperboard, to increase the column loading strength thereof to at least about'300 percent: said composition consisting essentially of a homogeneous admixture of about refined parafiin and about 50% limed rosin having about 4.5% lime content..

2. The process of compoundinga homogeneous ,water resistant and strength imparting impregnating composition adapted for impregnating corrugated paperboard, said process comprising the following successive steps; charging about 500 pounds of refined parafifin and about 500 pounds of limed rosin having about 4.5% lime content into a suitableivessehand heating .to .about325 degrees E, with some occasional mild agitation.

3. YA corrugated. paperboard sheet impregnated by ;im-

mersionfor at least about two minutes into a water,re

sistant and strength imparting impregnating composim.

tion, said composition consisting essentially of a homogeneous admixture of about 50% .refined parafiin and about 50% limed rosin having about 4.5% lime content;

heated to about 325 degrees F.

4. A waterresistant and strength'imparting imprcg-- nating composition for application .to'corrugated paperboard, to increase the column loadingstrength thereof to vat least about 300%;said composition consisting; essentially of a homogeneousadmixture of refined paraffintand limed rosin having about 4.5% lime content, wherein the content of refined parafi'in is within the range of e from about 45 to parts for each parts by weight.

ofithe composition.

5. The process of compounding a homogeneous. water resistant andstrength imparting impregnatingcomposition for impregnating corrugated paperboard, said process comprising the. following successive steps: charging about 1,000 pounds of refined paraflin and limed rosin having about 4.5% lime content into a suitable. vessel and heating to about 325 F. with some occasional mild agitation, wherein the content of refined parafiin is within the range of from about 450 to 550 pounds.

6. A corrugated paperboard sheet impregnated by immersionfor at "least about 2 minutes into a water resistant and strength imparting impregnating composition, said composition consisting essentially of a homogeneous admixture of refined paraifin and limed rosin having about 4.5% lime content, heated to about 325 F, wherein the content of refined paraffin is within the range of from about 45 to55 parts to each 100 parts by weight of the composition.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A WATER RESISTANT AND STRENGTH IMPARTING IMPREGNATING COMPOSITION FOR APPLICATION TO CORRUGATED PAPERBOARD TO INCREASE THE COLUMN LOADING STRENGTH THEREOF TO AT LEAST ABOUT 300 PERCENT: SAID COMPOSITION CONSISTING ESSENTIALLY OF A HOMOGENEOUS ADMIXTURE OF ABOUT 50% REFINED PARAFFIN AND ABOUT 50% LIMED ROSIN HAVING ABOUT 4.5% LIME CONTENT. 